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March 1956 v. H. FERGUSON INDUSTRIAL FURNACE SAFETY DEVICE INVENTOR. VERA/ N H -Ra asmv BY mm, diam Q VYZALM March 1956 v. H. FERGUSON INDUSTRIAL FURNACE SAFETY DEVICE 2 Sheets-Sheet 2 Filed May 27, 1952 IN V EN TOR.

Fan 0 5 av BY VEE/Va v y. M may n //".1 flrronueys INDUSTRIAL FURNACE SAFETY DEVICE Vernon H. Ferguson, Pittsburgh, Pa. Application May 27, 1952,,Serial No. 290,269

8 Claims. (Cl. 263 -1) This invention relates to safety devices for industrial furnaces, and more particularly to a method and means for preventing undesired combustible mixtures from accumulating in furnaces in explosive quantities.

It is not a rare occasion for a fuel fired industrial furnace to explode when a workman inserts a torch to light the furnace. Such explosions are due to the accumulation of fuel that leaked into the furnace while it was shut 01?. In a protective atmosphere type furnace, the chamber is completely filled with the protective atmosphere during operation because any, air inside the chamber has previously been purged or burned out. Since the protective atmosphere is not mixed with air it is not combustible, but if air leaks into the furnace and combines in proper proportions with the atmosphere therein before the furnace is brought up to temperature, there will be an explosion when the interior surfaces of the furnace reach the ignition point of the mixture. Sometimes such an explosive mixture will accumulate in the vestibule of a controlled atmosphere furnace, and when the furnace chamber door is opened the heat of the furnace causes an explosion. Wherever the word 'atmosphere is used herein, it means a gas or mixture of gases containing either no oxygen or insufficient oxygen for;v

burning.

It is among the objects of this invention to provide an industrial furnace safety device which will burn any undesired combustible mixture of gases in the furnace as it accumulates, which will signal in case the temperature of the mixture burner falls below the ignition temperature of such a mixture, whichwill not become overheated, and which may be formed to admit a controlled.

atmosphere to the furnace around the ignition element that burns the dangerous mixture of gases.

In accordance with this invention, an ignition element is placed in a furnace in a location where anundes'irable combustible mixture of gases may occur. This may be at the top ofsome types of furnaces and at the bottom of others. Means, preferably an electric circuit, is provided for maintaining the temperature of the element above the ignition temperature of such a mixture. Consequently, the mixture will burn as it forms and not be permitted to accumulate in suiiicient quantity to cause an explosion as it would when exposed to its ignition temperature. It is highly desirable that means be operatively connected with the ignition element for signaling if the temperature of the element falls below the ignitiontemperature of the combustible mixture. The ciri Patented Mar. 20, 1956 The invention is illustrated in the accompanying drawings, in which Fig. 1 is a side view of the ignition element projecting into afurnace and connected to the electric circuit of the safety device; Fig. 2 is a horizontal central section through the ignition element; Fig. 3 is a fragmentary vertical central section through the outer part of the ignition element; and Figs. 4, 5 and 6 are views similar to Figs. 1, 2 and 3, respectively, showing a modification of the safety device.

Referring to Figs. 1, 2 and 3 of the drawings, the

ignition element of the safety device includes. a ceramic tube 1 that extends into a furnace, either its chamber or vestibule depending on the circumstances, through an opening in its wall 2'. The inner end of the tube is closed and the entire tube is filled with refractory material 3 which has a high coefficient of thermal transmission. Embedded in this material is a pair of laterally spaced electrical conducting rods 4 and 5 of different lengths, one of which is disposed at the axis of the tube and extends to a point'near its inner end. The inner end of this rod is connected to an electric resistance coil 6 that encircles the rod and extends back along it to thei shorter'rod. The outer ends of these two rods project from the tube and are threaded and provided with nuts 7 for holding wires 8 that connect them to a terminal block 9. The block and nuts are disposed in a box 11 which is supported by a flanged ring 12 mounted on the outer,

end of the tube. This ring is screwed into the outer end of a sleeve 13, the inner end of which is slidably mounted ina flanged collar 14 secured to the furnace wall. Suitable sealing material 15 is forced against this collar and the sleeve by means of a nut 16 screwed on the outer. end of the collar. This arrangement permits the distance' that the tube projects into the furnace to be adjusted.

Connected to terminal block 9 is a pair of wires 18 which extend out of the bottom of box 11 throughan opening 19 and are connected to the secondary of a transformer 21. The primary of the transformer is connected by a Wire 22 to a circuitbreaker 23 and by a Wire 24 to the solenoid coil 26 of a coil current relay. The coil is connected by a wire 27 to the circuit breaker,

which is connected to an electric power line so that the resistance element 6 in tube 1 will be heated electrically. A" resistance is chosen which will heat the tube to a temperature high enough to ignite any combustible mixture that may start to accumulate in the furnace. This will prevent an explosive mixture from accumulating and causing an explosion.

In order to show that the ignition element is operating and is up to temperature, a light 28 is connected by a wire 29 to wire 27, and by a wire 30 toone contact of a switch-31 atvthe top of the relay. The other contact of this switch is connected by a wire 32 to Wire 22. As long as the ignition element is drawing the prescribed amount of current, solenoid 26 will be energized sufficiently tohold the relay armature 33 in its upper posi-' tion, where it holds a bridging contact member 34 against the contacts of switch 31 to complete the circuit through light 28. A second light 36 can be connected in parallel with the other light so that if one burns out the other will remain lighted. It will be seen that if for any reason,

except a short circuit, the ignition element begins to draw lesscurrent that it should, which would cause a re a horn or bell. This alarm is connected to the other side of the circuitbreaker by a wire 42, in which there is a normally closed switch43. T okeep the'al'arm'from sounding when this safety device is first turned on, this switch is held open manually for a few moments. It will be seen'that if an attendant does not observe .thelights going out in case the temperature of'the ignition element has fallen,'his attention will be called to the dangerous conditionby the audible alarm.

If this safety device is tobe used with a furnacethat is'heatedby gas, the ignition element, or several of them, is placed in theupper part of the furnace where anyleaking fuel gas would tend to accumulate. The safetydevice is always onguard to prevent the accumulation-chantingerous .amount of such gas, however, because .therh'ot ignitionelement .will burnthe gas as fast as.it:comes=in contact with that element. Of course, the ignition elementis intaddition to any pilot lights that the'furnace may have.

.The ignition .element'disclosed in Figs. 4, T5 hand-'6 .is designed primarily for 11S6\at'th6ibOttOm Of .a furnace which contains a protective atmosphere. Any vairlleakingiinto the furnace, being heavier than the .protective atmosphere, would accumulate and mix withthat atmos phere atzthebottom of -the furnace, so that is where the ignition element should .be located. In -this case the tube -51 extends intothe furnace through a passage '52 in wall 54. Theouter end of the tube-is mounted in a flan'gedring-"53 that is screwed in a sleeve 55 which is supported at its=inner end by acollar 56 attached'to-the furnace-wall. -By making the -wall passage considerably larger than the tube a space is provided between the sleeve andtube, and the-sleeve can be provided with an inlet opening to-which a-solenoid valve'57 can be connected. This valve is intendedto-be connected by a pipe'to the source of'protective atmosphere, and that atmcsphereis introduced into the furnace through the valve, sleeve and wall'passage.

*T he outer end of tube 51 is filled and sealed with refractory material 59 which supports two parallel insulated rods 60 and 61 of different lengths. 'The shorter of the two rods supports a metal block 62 just inside the .Ifurnace wall, and the other rod supports a metal block .63 near the inner endof the tube. These two blocks support the opposite ends of a silicon carbide resistor 64. Projecting into the outer end of this resistor is athermocouple '66, which extends out through the .end of the tube. The ends of the two rods are connected by wires 67 to a terminal block .68 in a box .69 supported ".by flanged ring '53.

A circuitbreaker'71, which is connected to .a .power line, has wires 72 and 73 attached to the centerterminals of a 'distributionpanel 74. Wire 72 is connected by a wire 76"to terminal block 68. The terminal blockalso is connectedby a wire 77 to one contact .of a solenoid operated switch 78, the other .contact of which is ,connected'by a wire 79 to wire 73 at the distributionpanel. The bridging member 81 for this switch is carried .bythe upper end'of an armature 82 which is .slidable in a solenoid coil83. One side of the coil is connected by.a wire 84 to'one side of the panel, and the other side of ,the coil is connected to the other side of the panel by means of wires 86 and'87 and a normally closed switch:88 in a relay 89, "forming part of a pyrometer (not shown), which is controlled by thermocouple 66 through wires-90. As long as current is flowing through the solenoid, the switch78 above it will remain closed and electric current willbe supplied to the resistor in theignition tube. .Ordinarily, a'trans'forrner is not necessary with this type of resistor. In case the ignition element starts to overheat, due toa'higher than usual temperature in the furnace, the relay switch'88 in the solenoid circuit will open, whereupon solenoid switch 78 will open and the current to the resistor will be cut off temporarily until switch 88 closes again.

The relay also contains a normally open bimetallic switch 92 that is connected by a wire 93 to one side of the 'distributionpanel, "and "by a'wire 94 "to "the solenoid coil 95 of a second relay. This coil is connected by a wire 96 to the panel. The switch 92 is preset to close, due to cooling of thermocouple 66, in case the temperature of the ignition element falls below the ignition temperature of a mixture of protective atmosphere and air that may occur in the bottom of the furnace. When this happens, vthe armature 97 of the second .relay is raised and causes a'bridging contact member 98 to close an upper switch'99:that is .connectedby wires 101 and 102 to an audible electric alarm 103.and to the panel, respectively. The other side of the alarm also is connected to the panel-bye wire 104. When switch 99 is closed, the alarm is sounded to warn that the ignition element no longer is functioning. The alarm circuit contains a normally closed switch 105 which is opened manually while the ignition element is first heating up.

In its normal lower position, the bridging member98 closes a lower switch .107 that is connectedby 'a wire 108 to wire 162, and by a .wire 109 to one side of solenoid valve 57. The.other side of the valve is connected by a wire 111 to the distribution panel. Current thus supplied to the valve holds it open, but when solenoid 95 isenergized to sound the alarm, the valve circuit is opened and the valve closes to cut off further delivery of atmosphere to the furnace. A. pair of signal lights 112 and 113 are shunted across the valve circuit to show bytheir burning that the valve is open. The circuit'may alsolcontain a normally closed switch 114 that can be opened manually any time that it is desired to close the valve.

It is important that the ignition element used in aprotective atmosphere .furnace be heated by other than a flame exposed to the atmospherein the furnace, because such a.flame would affect the protective atmosphere.

According to the provisions of the patent statutes, 1

have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, .within the scope of the appended claims, theinvention may be practiced otherwise than as specifically illustratedand described.

1 claim:

'1. An industrial furnace safety device comprising .an ignition element adapted to project into the lower partof a furnace, said .element including an electrical resistor sealed'in a tube, conduit means associated with said element for introducing apredetermined atmosphere into the furnace, ,a valve in said conduit means, an electric circuit connected with said resistor for maintaining the temperatureof'said'tube above the ignition temperature of a mixture of 'said atmosphere and air, whereby the mixture will'burn before it can accumulate in sufficient quan' tity to he exploded when exposed to its ignition temperature, and means responsive to the temperature of said tube for closing said valve if that temperature falls below said ignition temperature.

12. An industrial furnace safety device comprising an electric resistance ignition element adapted to be placed ina furnacein a location where an undesired combustible mixture of gases may.occur, an electric circuit connected with said element for maintaining its temperature above the ignition iemperature of said mixture, whereby any such mixture will burn before it can accumulatein sufficient quantity to be exploded when exposed to itsignition temperature, an electric alarm, an electric .circuit connected with-the alarm, an electric switch in the alarm circuit biased towards closedposition, and an electric coil .infthe Ifirst circuit for holding said switch open only as long as the said element draws enough current to keepjtabove saidiignition temperature.

'3. Anindustrialfurnace safety device comprising an lectric'res'istance ignition'elementadapted to be .placed in a furnace in a location where an undesiredcombustible mixture of gases may occur, an electric circuit connected with said element for maintaining its temperature above the ignition temperature of said mixture, whereby any such mixture will burn before it can accumulate in sufli cient quantity to be exploded when exposed to its ignition temperature, an electric alarm, an electric circuit connected with the alarm, a normally closed electric switch in the alarm circuit, an electric light, an electric circuit connected with said light, a normally open electric switch in the light circuit, and an electric coil in the first circuit for holding the alarm circuit switch open and the light circuit switch closed only as long as the temperature of said element is above said ignition temperature.

4. An industrial furnace safety device comprising an electric resistance ignition element adapted to be placed in a furnace in a location where an undesired combustible mixture of gases may occur, an electric circuit connected with said element for maintaining its temperature above the ignition temperature of said mixture, whereby any such mixture will burn before it can accumulate in suflicient quantity to be exploded when exposed to its ignition temperature, a normally closed switch in said circuit, and means responsive to the temperature of said element for opening the switch if that temperature exceeds a predetermined maximum.

5. An industrial furnace safety device comprising an electric resistance ignition element adapted to be placed in a furnace in a location where an undesired combustible mixture of gases may occur, an electric circuit connected with said element for maintaining its temperature above the ignition temperature of said mixture, whereby any such mixture will burn before it can accumulate in sufiicient quantity to be exploded when exposed to its ignition temperature, a switch in said circuit, a solenoid coil for closing the switch, a normally closed electric circuit connected with said coil, and means responsive to the temperature of said element for opening the last mentioned circuit if that temperature exceeds a predetermined maximum, whereby the first-mentioned switch will open.

6. An industrial furnace safety device comprising an electric resistance ignition element adapted to be placed in a furnace in a location Where an undesired combustible mixture of gases may occur, an electric circuit connected with said element for maintaining its temperature above the ignition temperature of said mixture, whereby any such mixture will burn before it can accumulate in sufficient quantity to be exploded when exposed to its ignition temperature, an electric alarm, an electric circuit connected with the alarm, a normally open electric switch in the alarm circuit, an electric light, an electric circuit connected with said light, a normally closed electric switch in the light circuit, a solenoid coil associated with said switches, a normally open electric circuit connected with said coil, and means responsive to the temperature of said element for closing the last-mentioned circuit if that temperature falls below said ignition temperature, whereby said coil will open the light circuit switch and close the alarm circuit switch.

7. The combination with an industrial furnace having a passage through its wall near its bottom, of a conduit connected to the outer end of said passage for delivering a predetermined atmosphere to the inside of the furnace, an ignition element extending through said passage and projecting from both ends of it, the outer end of said element being supported by said conduit spaced from the walls of the conduit and passage, and means for maintaining the temperature of the ignition element above the ignition temperature of a mixture of said atmosphere and air, whereby the mixture will burn before it can accumulate in sufficient quantity to be exploded when exposed to its ignition temperature.

8. The combination with an industrial furnace having a passage through its wall near a location where an undesirable combustible mixture of gases may occur, of a sleeve mounted on said wall around the outer end of the passage, a ring adjustable axially in the outer end of the sleeve, a tube extending through the sleeve and passage and into the furnace and having its outer end mounted in said ring, an electrical resistor sealed in the tube inside the furnace, and an electric circuit connected with said resistor for maintaining the temperature of the tube above the ignition temperature of said mixture, whereby any such mixture will burn before it can accumulate in suflicient quantity to be exploded when exposed to its ignition temperature.

References Cited in the file of this patent UNITED STATES PATENTS 1,535,240 Morris Apr. 28, 1925 1,670,819 Morris et al May 22, 1928 2,095,253 Heyroth Oct. 12, 1937 2,474,941 Hasselhorn et al. July 5, 1949 2,487,752 Cohn Nov. 8, 1949 2,506,913 Baker May 9, 1950 2,575,113 Lennox Nov. 13, 1951 

1. AN INDUSTRIAL FURNACE SAFETY DEVICE COMPRISING AN IGNITION ELEMENT ADAPTED TO PROJECT INTO THE LOWER PART OF A FURNACE, SAID ELEMENT INCLUDING AN ELECTRICAL RESISTOR SEALED IN A TUBE, CONDUIT MEANS ASSOCIATED WITH SAID ELEMENT FOR INTRODUCING A PREDETERMINED ATMOSPHERE INTO THE FURNACE, A VALVE IN SAID CONDUIT MEANS, AN ELECTRIC CIRCUIT CONNECTED WITH SAID RESISTOR FOR MAINTAINING THE TEMPERATURE OF SAID TUBE ABOVE THE IGNITION TEMPERATURE 